Cisco CCENT/CCNA ICND1 100-101 Official Cert Guide

1. TCP/IP and OSI Models: Blueprints for Network Communication

A networking model, sometimes also called either a networking architecture or networking blueprint, refers to a comprehensive set of documents.

Architectural Frameworks. Networking models like TCP/IP and OSI provide a structured approach to understanding and building computer networks. They define protocols, standards, and layers, ensuring that different network components can communicate effectively.

TCP/IP Model. The TCP/IP model, with its application, transport, network, and link layers, is the dominant model used in modern networks. It focuses on practical implementation and interoperability. The OSI model, while not as widely implemented, offers a valuable reference point for understanding network functions and terminology.

OSI Model. The OSI model, with its seven layers (application, presentation, session, transport, network, data link, and physical), provides a detailed framework for understanding network communication. It helps categorize protocols and functions, facilitating troubleshooting and design.

2. Ethernet LANs: The Foundation of Local Networks

The term Ethernet refers to a family of LAN standards that together define the physical and data link layers of the world’s most popular wired LAN technology.

Wired Connectivity. Ethernet LANs, using cables and switches, form the backbone of most local networks. They offer reliable, high-speed connections for devices within a limited geographical area.

Physical Layer Standards. Ethernet encompasses a variety of physical layer standards, each specifying different cabling types, speeds, and distances. Common standards include 10BASE-T, 100BASE-T, and 1000BASE-T, each with its own characteristics and limitations.

Data Link Layer. Despite the variety of physical layer standards, Ethernet maintains a consistent data link layer protocol. This ensures that all devices can communicate using a common frame format, regardless of the underlying physical medium.

3. WAN Fundamentals: Connecting Distant Networks

That job is simply this: moving data from one device to another.

Bridging the Distance. WANs connect networks over long distances, enabling communication between geographically separated locations. They rely on leased lines, Ethernet WANs, and Internet access technologies.

Leased Lines. Leased lines provide dedicated, point-to-point connections between sites, offering guaranteed bandwidth and reliability. They are often used for critical business applications.

Internet Access. Technologies like DSL and cable Internet provide WAN connectivity for homes and small offices, leveraging existing infrastructure to deliver high-speed Internet access.

4. IPv4 Addressing: The Logic Behind Network Communication

IP defines addresses for several important reasons.

Logical Addressing. IPv4 addressing provides a logical addressing scheme that enables devices to be uniquely identified on a network. This addressing scheme is crucial for routing data packets to the correct destinations.

IP Address Structure. IPv4 addresses are 32-bit numbers, typically written in dotted-decimal notation. They are divided into network and host portions, with the network portion identifying the network and the host portion identifying the specific device on that network.

Routing Protocols. Routing protocols, such as OSPF, enable routers to dynamically learn about network topology and exchange routing information. This allows routers to make informed decisions about the best paths for forwarding data packets.

5. TCP and UDP: The Unsung Heroes of Data Delivery

Transport layer protocols provide services to the application layer protocols that reside one layer higher in the TCP/IP model.

Transport Layer Protocols. TCP and UDP are the two primary transport layer protocols in the TCP/IP model. They provide essential services for delivering data between applications.

TCP. TCP offers reliable, connection-oriented communication, ensuring that data is delivered accurately and in the correct order. It provides error recovery, flow control, and congestion management.

UDP. UDP offers a simpler, connectionless communication model, sacrificing reliability for speed and efficiency. It is often used for applications that require low latency, such as streaming media and online gaming.

6. LAN Switching: Building Efficient Local Networks

LAN switching concepts

Switching Logic. LAN switches forward Ethernet frames based on the destination MAC address, learning MAC addresses dynamically and building a MAC address table. This allows switches to efficiently direct traffic only to the intended recipient.

Collision and Broadcast Domains. Switches create separate collision domains for each port, reducing collisions and improving network performance. They also segment the network into broadcast domains, limiting the scope of broadcast traffic.

VLANs. Virtual LANs (VLANs) allow network administrators to logically segment a physical network into multiple broadcast domains. This enhances security, improves network performance, and simplifies network management.

7. Cisco Switch Operations: Accessing and Configuring the CLI

Accessing the Cisco Catalyst 2960 Switch CLI

Command-Line Interface. The Cisco IOS CLI provides a text-based interface for configuring and managing Cisco switches. It offers a powerful and flexible way to control switch behavior.

Accessing the CLI. The CLI can be accessed through various methods, including the console port, Telnet, and SSH. Each method has its own advantages and disadvantages in terms of security and convenience.

Configuration Modes. The CLI operates in different modes, each with its own set of commands and privileges. User EXEC mode allows basic monitoring, while privileged EXEC mode enables configuration changes.

8. Switch Configuration: Securing and Managing Ethernet Networks

Configuration of Features in Common with Routers

Security First. Securing the switch CLI is crucial for protecting the network from unauthorized access. This involves setting strong passwords, disabling unnecessary services, and limiting access to authorized users.

Interface Configuration. Configuring switch interfaces involves setting parameters such as speed, duplex, and VLAN membership. These settings determine how the switch forwards traffic and interacts with connected devices.

Port Security. Port security enhances network security by limiting the number of MAC addresses allowed on a port. This prevents unauthorized devices from connecting to the network.

9. VLANs: Segmenting Networks for Efficiency and Security

Virtual LAN Concepts

Logical Segmentation. VLANs create logically separate networks within a physical network. This allows administrators to group devices based on function, department, or security requirements.

Trunking. VLAN trunking enables multiple VLANs to share a single physical link between switches. This is achieved by adding VLAN tags to Ethernet frames, allowing switches to identify the VLAN to which each frame belongs.

Inter-VLAN Routing. To enable communication between devices in different VLANs, a router or Layer 3 switch is required. This device performs inter-VLAN routing, forwarding traffic between the different VLAN subnets.

10. Troubleshooting Ethernet LANs: Diagnosing and Resolving Network Issues

Perspectives on Network Verification and Troubleshooting

Organized Approach. Troubleshooting Ethernet LANs requires a systematic and organized approach. This involves gathering information, isolating the problem, and identifying the root cause.

Troubleshooting Tools. Tools like CDP, show commands, and ping can be used to verify network status, identify connectivity problems, and analyze network topology.

Common Issues. Common Ethernet LAN issues include interface status problems, speed and duplex mismatches, VLAN misconfigurations, and trunking errors.

11. IPv4 Addressing and Subnetting: Dividing Networks for Optimal Use

Introduction to Subnetting

Subnetting. Subnetting is the process of dividing a Class A, B, or C network into smaller, more manageable subnets. This allows for more efficient use of IP addresses and improves network performance.

Subnet Mask. The subnet mask defines the boundary between the network and host portions of an IP address. It determines the number of subnets and the number of hosts per subnet.

VLSM. Variable-Length Subnet Masks (VLSM) allow for different subnet sizes within the same network. This provides greater flexibility in allocating IP addresses and optimizing network resources.

12. IPv4 Services: Enhancing Network Functionality

IPv4 Services

Access Control Lists. Access Control Lists (ACLs) are used to filter network traffic based on various criteria, such as source and destination IP addresses, port numbers, and protocols. They enhance network security by controlling access to network resources.

Network Address Translation. Network Address Translation (NAT) enables devices with private IP addresses to communicate with the Internet. It translates private IP addresses to public IP addresses, allowing multiple devices to share a single public IP address.

NTP. Network Time Protocol (NTP) synchronizes the time-of-day clocks on network devices. This is crucial for accurate logging and troubleshooting.

Last updated: March 13, 2025